Trench isolation is a commonly employed scheme for achieving sidewall isolation in a variety of semiconductor architectures, such as silicon on insulator (SOI), including separation by implanted oxygen (SIMOX) and bonded wafer technologies, as well as PN junction isolation structures. Within the semiconductor wafer (e.g. silicon substrate), the trench is coated with an insulator material, typically oxide, and filled with a material such as polysilicon, which is often electrically floating. Although a bias voltage may sometimes be applied to the poly-fill material in order to control parasitic sidewall MOS devices (for which the polysilicon acts as a gate), the essential function of the trench is to provide isolation among the islands of the substrate. Interconnect among circuit device regions is effected by way of in situ diffusions within the islands and conductor tracks overlying a topside insulator layer.